This invention relates to a method and apparatus for fastening one element to another. More particularly, this invention relates to an orthopedic method and fastener for fixing tendinous ligaments to associated structures. Still more particularly, this invention relates to such a fastener suitable for use in construction, but particularly adapted for orthopedic work, which is structurally adapted to be driven into the supporting structure in a manner similar to a nail, and secured therein by rotating the device through a predetermined angle. Still more particularly, this invention relates to such a fastener having threads circumferentially located only on a limited circumferential portion of the shank of the fastener, the remaining circumferential portion being unthreaded.
In general, there are a number of applications in which a threaded fastener, such as a conventional screw, having threads substantially entirely about the circumference of the shank of the fastener, is completely satisfactory for its intended purpose. In such applications, the threaded fastener is rotated substantially continuously to advance the fastener into the support structure. For some occasions, such a technique may not be completely satisfactory. For example, in a wood construction situation having a number of screws to be fastened, it would be advantageous to be able to drive the fastener into the fastened members for purposes of quickly locking the fastener by rotation, rather than continuously rotating the screw through multiple revolutions.
In the orthopedic field of use, such a device has significant advantages. In general, in the present methods of fixing tendinous ligaments with small fragments of bone to large bones, particularly cancellous bones, screws have traditionally been the method of choice for fixation. In part, this occurs because the cortical bone is quite hard and more likely to split if the fastener is driven into it. While orthopedic staples of various types of construction have also been used, there have been advantages and disadvantages. In a typical staple construction, a groove in the top portion of the staple is used by a driver to grip the staple. Such staples are barbed to retard the staples from pulling free from the bone, but it has continued to be a problem in that frequently such staples pull free from the bone. A disadvantage in the use of the staple resides in the fact that the size of the driver is large when trying to apply a staple into a small incision such as in an interior portion of a shoulder and it can be difficult in that location to remove the staple because of the holding barbs. Thus, the more secure the barbs make the staple in the bone, the more difficult that structure makes the process for extracting the staple. Moreover, the tines can spread and bend as they are driven, sometimes causing difficulties in that the staple will penetrate a joint.
Thus, in orthopedics, an advantage of the screw is that it will not retreat and it can be easily removed by counter-rotating the screw. However, a screw is not an ideal fixation device for a tendon or ligament because the head of the screw does not tend to hold them well and it is slower to insert because of the operation time to rotate the screw to advance the fastener according to the pitch of the screw threads. Moreover, in soft tissue or with a deep incision, it is often quite difficult to locate a predrilled pilot hole for insertion of a screw.
Still another type of orthopedic fastener is a nail which can be driven quite quickly and can be barbed. However, an orthopedic nail is sometimes difficult to remove and perhaps the most difficult to drive because it is not attached to a firm, self-holding driver.
Thus, it is a general problem and a particular problem in the field of orthopedics to develop a fastener which is as quick to drive as a nail but easier to remove than a screw.
Accordingly, it is an object of this invention to provide such a fastener which features threads placed on a limited circumferential portion of the shank of the fastener so that the fastener can be driven and rotated a predetermined amount, such as a quarter of a turn, to complete the fastening process and to permit removal by counter-rotating the device a quarter of a turn.
It is an additional object of the invention to provide a method for securing two objects together by driving a fastener of the type described according to the invention into an object to be fastened through another fastening object in a manner similar to driving a nail, and securing the driven fastener by a limited rotation through a predetermined angular displacement corresponding generally to the angular distribution of a plurality of sets of threads about the circumference of the shank.
It is an additional general object of this invention to provide a fastener of the type described particularly suited for use as an orthopedic fastener.
These and other objects of the present invention will become apparent from the detailed description of the various embodiments of the invention which follow, taken in conjunction with the accompanying drawings.